Lip seal with inversion prevention feature

ABSTRACT

A dynamic shaft seal assembly is provided including a dynamic seal for engaging a rotary shaft. The dynamic seal includes a mounting portion that is mounted within a casing and has an axially extending barrel portion extending from a radially inner end of the mounting portion. The axially extending barrel portion terminates in a radially extending leg portion which extends inwardly from an end of the axially extending portion. A generally conically shaped seal portion extends from an end of the radially extending portion and the seal portion includes a radially inner face engaging the shaft and a radially outer face having a stiffening bead integrally formed thereon. The mounting portion defines a bumper spaced from the axially extending barrel portion by a gap distance that is designed to prevent the seal lip from inverting under sustained high pressure or pressure spikes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/032728,filed Sep. 20, 2013, which is a divisional of U.S. application Ser. No.12/410067, filed Mar. 24, 2009 (now U.S. Pat. No. 8,590,903, issued Nov.26, 2013), the disclosures of which are incorporated herein byreference.

FIELD

The present invention relates to “lay-down” dynamic shaft seals, andmore particularly, to a dynamic shaft seal design to reduce the seal'storque, propensity for bell mouthing, and for providing improved shaftfollowability and improved ability to withstand internal excessivepressure or vacuum. The “lay-down” seal for their function rely onhydrodynamic pumping features as opposed to “standard” or“point-contact” seals that rely primarily on the intrinsic ability ofsome elastomers to pump in properly designed seals.

BACKGROUND AND SUMMARY

Rotary shaft seals have been utilized in machinery, the automobileindustry, as well as other industries. Three major problems associatedwith seals designed to have substantial contact areas between the shaftand the lip of the seal are “bell mouth,” the shaft followability at lowtemperatures, and oil carbonization in the pumping grooves due to localtemperature rise causing increased torque. “Bell mouth” is a phenomenonassociated with the lift of the edge of the lip from the shaft. Theproblem is extenuated for highly incompressible materials, like rubberand PTFE. The ability of the seal to follow the shaft when the shafteither wobbles or is misaligned is also important to a seal design.

The present invention is designed to reduce seal torque, the propensityfor “bell mouthing” and also provides for improved shaft followabilityat low temperatures. The dynamic seal includes an annular mountingportion which is capable of being mounted to a casing which surrounds arotary shaft. The seal includes an axially extending portion extendingfrom the radially inner end of the mounting portion, with a radiallyextending portion extending inwardly from an end of the axiallyextending portion. A generally conically shaped seal portion extendsfrom an end of the radially extending portion with the seal portionincluding a radially inner face provided with a plurality of grooves orribs and a radially outer face having a special bead defining a regionof increased thickness. The bead acts as an integral spring to controlthe gap between the essentially conical portion of the seal and theshaft as well as a means for counteracting the “bell mouthing”propensity of the seal portion. The bead can have different shapesincluding a triangular-cross section or a rounded bead, as well as otherconfigurations which are deemed to be appropriate. The bead ispositioned slightly away from the edge of the lip to provide asufficient lip “lay-down” to properly engage the hydrodynamic pumpingfeatures, which would normally be located on the lip contact are betweenthe edge of the seal and the bead. The flexibility of the axiallyextending portion of the seal provides an improvement in the shaftfollowability due to the generally cylindrical shape of the axiallyextending portion having lower bending stiffness. Therefore, if thematerial of the seal does not have sufficient intrinsic elasticity,making the axially extending portion of the seal in a generallycylindrical shape improves the overall shaft followability. The lengthand the wall thickness of the cylindrical portion allow one to controlthe degree of flexibility to match the application requirements.

The mounting portion is provided with a bumper structure to prevent theseal lip from inventing during sustained high pressures or pressurespikes. The bumper is spaced from the axially extending portion by a gapdistance that limits the deflection of the axially extending portion to60 degrees or less from parallel to the central axis. Defined analternative way, the gap distance G should limit the radially extendingportion from becoming parallel to the shaft. The bumper structure cantake many forms, as detailed herein.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a detailed cross-sectional view of the dynamic seal accordingto the principles of the present disclosure;

FIG. 2 is a cross-sectional view of second embodiment of the dynamicseal according to the principles of the present disclosure;

FIGS. 3A-3C illustrate a cross-sectional view of a third embodiment ofthe dynamic seal according to the principles of the present disclosure;

FIG. 4 is a cross-sectional view of a fourth embodiment of the dynamicseal according to the principles of the present disclosure;

FIG. 5 is a cross-sectional view of a fifth embodiment of the dynamicseal according to the principles of the present disclosure;

FIG. 6 is a cross-sectional view of a sixth embodiment of the dynamicseal according to the principles of the present disclosure; and

FIG. 7 is a cross-sectional view of a seventh embodiment of the dynamicseal according to the principles of the present disclosure.

DETAILED DESCRIPTION

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

With reference to FIG. 1, a dynamic seal 10, according to the principlesof the present disclosure, will now be described. The dynamic seal 10includes a mounting portion 12 which is designed to be engaged within abore of an outer housing 14. It should be noted that the mountingportion 12 can take on many shapes and can include an insert 15 whichcan be made from metal or plastic or other rigid material and can havean “L” or other cross-sectional shape.

The dynamic seal 10 includes an axially extending barrel portion 16extending from a radially inner end 12A of the mounting portion 12. Theaxially extending barrel portion 16 is preferably generally cylindricalin shape although other shapes, such as conical or a convoluted curveshape, can also be utilized. The dynamic seal 10 includes a radiallyextending portion 18 extending inwardly from a distal end 16B of theaxially extending barrel portion 16. A generally conically shaped sealportion 20 extends from a radially innermost end 18A of the radiallyextending portion 18. The axially extending barrel portion 16 extends ina first axial direction from mounting portion 12, while the generallyconically shaped seal portion 20 extends from the radially innermost end18A of radially extending portion 18 in an axial direction opposite tothe first axial direction. The seal portion 20 includes a radially innerface 22 which may be provided with a plurality of grooves 24. Thegrooves 24 can be helical in shape or can take other known forms. Thegrooves 24 provided in the radially inner surface 22 of the seal portion20 are capable of retaining oil therein in order to provide lubricationbetween the dynamic shaft seal 10 and a rotary shaft and also canprovide a pumping function for returning leaked oil to the oil side ofthe seal. A radially outer face 26 of the conically shaped seal portion20 can be provided with a stiffening bead 28 defining a region ofincreased thickness. The stiffening bead 28 can have different shapes,including a triangular shape, as shown, or can have rounded or othershape configurations. The stiffening bead 28 is positioned slightly awayfrom the end edge 20A of the lip 20 to allow a proper contact area todevelop. The bead 28 serves as an integrally formed spring for biasingthe sealing lip 20 against the rotary shaft for counteracting bellmouthing of the sealing lip 20. Normally, the seal lip-free edge facesthe oil side. However, reverse mounting is also possible. In that case,the design of the spiral grooves have to be accommodated appropriatelyto pump in the direction of the oil sump.

The improvement in the shaft followability of the dynamic seal 10 isprovided by the axially extending barrel portion 16. The generallycylindrical shape of the barrel portion 16 has a lower bending stiffnessthan other structures; therefore, the axially extending barrel portion16 is able to readily account for a wobbling shaft or a shaft that isout of center relative to the housing 14.

It should be noted that if desired or advantageous in a particularapplication, the dynamic shaft seal 10 of the present disclosure canoptionally include one or more axial or radial dirt protective lips 30as are known in the art, one of which is shown, for example, in FIG. 1.The optional dirt protective lip 30 can be formed integrally with thedynamic shaft seal, or can be formed separately therefrom and attachedthereto, and can have any of a number of shapes or configurations, as isalso known in the art. In addition, the lip 30 can protrude transverselyfrom the dynamic shaft seal in any of a number of directions, including,but not limited to, the exemplary angular relationship protrudinggenerally radially away and axially away from the shaft-engaging sealingcomponents, as shown, for example, in FIG. 1.

The radially extending leg portion 18 can be straight, as shown, oralternatively, can be provided with a convoluted shape. As illustratedin FIG. 2, the generally conically shaped seal portion 20 is designed totake on a generally cylindrical form when deformed by the rotary shaft14 and the leg 18 is designed to apply pressure to the heel portion 32of the seal portion 20. The leg portion 18 acts radially on the end 16Aof the barrel portion 16 which has a length sufficient to allow thebarrel portion 16 to flex radially inwardly and outwardly to accommodatefor shaft wobble or shaft misalignment. The length of the leg portion isderivative from the length of the seal portion, the amount of theseal-to-shaft interference, and the distance between the casing and theshaft.

The dynamic shaft seal 10 of the present invention can be utilized forisolating an oil environment from an air environment disposed on eitherside of the dynamic seal 10. In order to optimize the seal design, thelength of the seal portion 20 and the stiffness of the bead 28(geometry, thickness, material, etc.) are specifically chosen forparticular applications. Furthermore, the thickness of the radiallyextending leg portion 18 is also specifically designed to providesufficient pressure on the heel 32 of the seal portion 20. The thicknessand length of the barrel portion 16 should also be specifically designedto accommodate the requisite flexibility of a particular application.The seal material composition for the dynamic seal can include plastic,rubber, or any of a wide variety of known elastomers, such as PTFE, TPE(thermoplastic elastomers), TPV (thermoplastic vulcanizates), andFlouroprene™ material, a composition described in U.S. Pat. No.6,806,306. An additional embedded spring in the bead may be utilized inorder to extend the life of the seal due to the fact that creep canoccur in thermoplastic or elastomeric materials which prevents thematerial from regaining its original properties. The spring would thenprovide an additional radial load on the seal surface that thethermoplastic material is incapable of maintaining over a long life. Thespring can also improve the robustness of the seal required incontaminated environments. Instead of imbedding, the spring can beplaced in a specially designed and manufactured spring groove aftercompletion of the molding operation (as is normal with other radial lipseals).

A bumper portion 40 is disposed on the mounting portion 12 and is spacedradially outward from the axially extending barrel portion 16 by a gapdistance G. With the design of the present disclosure, the dynamic seal10 is capable of withstanding excessive internal pressure or vacuum. Inthe case of excessive internal pressure being applied to the dynamicseal 10, the axially extending barrel portion 16 which radially overlapsthe seal portion 20 provides a radial spring acting upon the radiallyextending portion 18 to limit the deformation in the seal portion 20.The axially extending barrel portion 16 contacts the bumper portion 40that limits the axial movement of radially extending portion 18, thuslimiting the axial movement of the seal portion 20 to prevent inversionthereof. The bumper portion 40 can be integrally formed from the sealmaterial as a series of discrete bumpers 40 a having a space 42 disposedbetween adjacent bumpers, as illustrated in FIG. 1. Alternatively, thebumper 140 can be formed as a continuous bumper around the circumferenceof the dynamic seal 110, as illustrated in FIG. 2. The gap spacing Gbetween the axially extending barrel portion and the bumper portion 40,140 is designed to allow limited radial movement of the radiallyextending portion 18 while preventing sufficient radial movement topermit the seal lip 20 from being inverted (i.e. flipped up-side-down)under sustained high pressures or pressure spikes. Preferably, the gapdistance G limits the deflection of the axially extending portion to 60degrees or less from parallel to the central axis. More particularly,the gap distance G limits the deflection of the axially extendingportion to less than 45 degrees, and even more particularly to less than30 degrees from parallel to the central axis. Defined an alternativeway, the gap distance G should limit the radially extending portion 18from becoming parallel to the central axis.

As a further alternative, as illustrated in FIGS. 3A-3C, a bumperstructure 240 for a dynamic seal 210 can be formed by the insert case215. In particular, the insert case 215 can include an arm portion 242which can be extended axially from the insert case 215 during themolding process and can be subsequently bent radially inward asillustrated by FIG. 3B to a final position as illustrated in FIG. 3C,wherein a gap G is provided between an end portion 244 of the armportion 242 and the distal end 16A of the axially extending portion 16of the dynamic seal 210. The arm portion 242 acts as a bumper to limitthe radial movement of radially extending portion 18, thus limiting theaxial movement of the seal portion 20 to prevent inversion thereof. Itshould be noted that the arm portion 242 can be a continuous radiallyinwardly extending ring, or a series of discrete tabs that are spacedfrom one another.

As a further alternative, as illustrated in FIG. 4, a bumper structure340 for a dynamic seal 310 can be formed by a secondary insert case 315that is received inside insert 15. The secondary insert case 315 can beL-shaped and can include an axially extending portion 315 a and aradially inwardly extending portion 315 b. The axially extending portion315 a is friction fit within L-shaped insert 15. The radially inwardlyextending portion 315 b of the secondary insert case 315 is spaced fromthe radially extending portion 18 of the seal by a gap distance G, asdefined herein. The radially inwardly extending portion 315 b defines abumper to limit movement of the radially extending portion 18 to preventinversion of the seal portion 20.

As a further alternative, as illustrated in FIG. 5, a bumper structure440 for a dynamic seal 410 can be formed by the insert case 415. Inparticular, the insert case 415 can have a generally “C” shapedcross-section with an outer portion 415 a connected to an inner portion415 b by an intermediate radially extending portion 415 c. The insertcase 415 can be overmolded within the mounting portion 412 of thedynamic seal 410. The inner surface 442 of the inner portion 415 bdefines a bumper structure 440 spaced from the axially extending portion16 by a gap distance G as defined, to limit the radial movement of theradially extending portion 18 to prevent inversion of the seal lip 20.

As a further alternative, as illustrated in FIG. 6, a bumper structure540 for a dynamic seal 510 can be formed by the insert case 515. Theinsert case 515 can include an axially extending outer portion 515 a, aradially inwardly extending portion 515 b, and an axially extendinginner portion 515 c. The inner portion 515 c of the insert case 515defines an inner surface 542 that provides a bumper structure 540 spacedfrom the axially extending portion 16 by a gap distance G, as defined,to limit the radial movement of the radially extending portion 18 toprevent inversion of the seal lip 20.

As a further alternative, as illustrated in FIG. 7, a series ofreinforcing gussets 640 are provided for strengthening the axiallyextending portion 616 of the dynamic seal 610. The gussets 640 can bespaced from each other by a distance x and are formed on the radiallyouter side of the axially extending portion 616. The gussets 640reinforce the axially extending portion 616 to limit the radial movementof the radially extending portion 18 to prevent inversion of the seallip 20.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

What is claimed is:
 1. A dynamic seal, comprising: an annular mountingportion; an axially extending portion extending in a first axialdirection from said mounting portion, said mounting portion defining abumper surface spaced radially outward from said axially extendingportion by a gap distance, wherein said bumper surface is formed from ametal insert over-molded within said mounting portion; a radiallyextending portion extending radially inwardly from an end of saidaxially extending portion; a generally conically shaped seal portionextending from an end of said radially extending portion in a directionopposite said first axial direction, said seal portion including aradially inner face adapted to engage a rotary member, wherein said gapdistance prevents the axially extending portion from deflecting morethan 60 degrees from parallel with a central axis.
 2. The dynamic sealaccording to claim 1, wherein said insert includes an axially extendingportion disposed within said mounting portion and an arm portionextending from said axially extending portion that is bent radiallyinward and defines said bumper.
 3. The dynamic seal according to claim1, wherein said insert includes an axially extending bumper portiondefining said bumper.
 4. The dynamic seal according to claim 3, whereinsaid insert includes a C-shaped cross-section.
 5. The dynamic sealaccording to claim 3, wherein said insert includes a radially extendingportion extending radially outwardly from said axially extending bumperportion toward an outer surface of said mounting portion.
 6. The dynamicseal according to claim 5, wherein said insert includes an axiallyextending portion extending from an outer end of said radially extendingportion and reinforcing said mounting portion.